A Topslide DRO for a Boxford Lathe
Model Engineers' Workshop|March 2020
Egret fits a removable readout to his lathe
Egret

I have recently ordered two axis DRO equipment for my 1984 Boxford VSL lathe but shied away from including a reader for the top slide, as this would require accurate angular measurement of the top slide setting and associated trigonometry to give a readout in X and Y axes. This means most hobby users would only perform the summing function when the top slide is set at (or very close to) zero degrees.

With the top slide set at 0 degrees a reader can be used. Consoles such as the Easson ES12C 3 axis unit incorporates software to sum two inputs and so are able to use three inputs and combine two of those to give a two-axis readout. For angular settings of the top slide the summing can only be done by the operator using trigonometry, in which case one might prefer a cheap stand-alone reader on the topslide, avoiding the need for signal cabling and minimising costs.

I therefore decided to make an experimental DRO using a cheap digital vernier with the objective of showing me how useful a DRO is on the topslide, seeing how much it gets in the way, seeing whether it can be securely and accurately fitted without drilling and tapping into the lathe. Crucially it needs to be quick and easy to fit and remove.

Lessons learned would help me evaluate the merits and feasibility of making a removable reader to work with the Easson 3 axis Readout.

The fixing method adopted has proven amazingly successful and works very well at the most useful ‘zero degrees’ setting. While it stops the topslide being set at an angle, it can be removed so quickly that this really is not an issue. Furthermore, it does not interfere with routine machining operations as it is well out of the way of both the toolpost and the topslide handwheel.

I was so pleased with the outcome that I thought others might like to try the approach.

Adapting the Vernier

The vernier used was a 150mm Powerfix vernier, shown dismantled in photo 2, which I had lying unused in the workshop.

The reader head comprises two main parts. A shallow stainless steel channel or carriage and a plastic top casing which holds the electronics.

The reader head is easily removed from the caliper blade by removing the label from the back of the head, unscrewing four self-tapping screws and removing the clamping screw from the side of the carriage. The two screws retaining the stop bar at the end of the blade were also removed so that the reader head could be slid off the end of the arm.

When removing the carriage take care to note which way round the pressure leaf spring is fitted. It is located at one end over a pin at the end of one of the adjusting screws. Also take care when refitting the carriage as the top edge of each of the channel sides has a very thin strip which hooks over the arm and is very vulnerable to damage during reassembly.

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